GERM-LINE AND EMBRYONIC EXPRESSION OF FEX, A MEMBER OF THE DROSOPHILAF-ELEMENT RETROTRANSPOSON FAMILY, IS MEDIATED BY AN INTERNAL CIS-REGULATORY CONTROL REGION

The F elements of Drosophila melanogaster belong to the superfamily of Long interspersed nucleotide element retrotransposons. To date, F ele ment transcription has not been detected in flies. Here we describe th e isolation of a member of the F-element family, termed Fex, which is transcribed in specific cells of the female and male germ lines and in various tissues during embryogenesis of D. melanogaster. Sequence ana lysis revealed that this element contains two complete open reading fr ames coding for a putative nucleic acid-binding protein and a putative reverse transcriptase. Functional analysis of the 5' region, using ge rm line transformation of Fex-lacZ reporter gene constructs, demonstra tes that major aspects of tissue-specific Fex expression are controlle d by internal cis-acting elements that lie in the putative coding regi on of open reading frame 1. These sequences mediate dynamic gene expre ssion in eight expression domains during embryonic and germ line devel opment. The capacity of the cis-regulatory region of the Fex element t o mediate such complex expression patterns is unique among members of the long interspersed nucleotide element superfamily of retrotransposo ns and is reminiscent of regulatory regions of developmental control g enes.